1. Field of the Invention
The present invention relates to a mechanical seal device which is preferably used for a shaft seal of centrifugal pump, agitator, etc.
2. Description of the Related Art
There exists a mechanical seal device which seals a high viscosity fluid and the like under a condition that fluid pressure within the apparatus is frequently changed in operation. As for a mechanical seal device used under such condition, for instance, a double mechanical seal device, wherein one O-ring for a secondary seal is sandwiched with a step formed stationary ring and a step formed housing, is known (See Japanese Unexamined Patent Application No. 2003-97728 and the like).
Mechanical seal device of conventional art, comprising the secondary seal O-ring sandwiched between step part of stationary ring and step part of housing, is capable of sealing fluid within the apparatus even when pressure of fluid within the apparatus varies. Namely, mechanical seal device having such structure is capable of pressing stationary ring toward rotary ring even under a positive pressure in which pressure of fluid within the apparatus is higher than that of fluid outside the apparatus, or even under a counter pressure in which pressure of fluid within the apparatus is lower than that of fluid outside the apparatus.
However, with the mechanical seal device comprising O-ring sandwiched between step part of stationary ring and that of housing, when fluid pressure changes between positive pressure and counter pressure, O-ring moves in a room surrounded by step part of stationary ring and that of housing. Namely, O-ring moves toward outside of the apparatus when fluid pressure is positive pressure, while O-ring moves toward inside of the apparatus when fluid pressure is counter pressure.
Accordingly, a problem occur with the mechanical seal device of conventional art that O-ring itself and stationary ring or step part of housing which contact with O-ring are worn by the movement of O-ring, and reduces life expectancy of the mechanical seal device. Particularly when used under a condition that fluid pressure frequently switches between positive pressure and counter pressure, O-ring and parts contacting O-ring are rapidly worn; and that problems such as leakage and reduced life expectancy are likely to occur.